1. Field of the Invention
One embodiment of the present invention relates to semiconductor devices and display devices.
2. Description of the Related Art
Display devices with higher value have been developed accompanying spread of large-sized display devices such as liquid crystal television. In particular, a technology of using transistors whose conductivity types are the same as each other in a driver circuit has been actively developed (see Patent Document 1).
FIG. 23 illustrates a driver circuit described in Patent Document 1. The driver circuit described in Patent Document 1 includes transistors M1, M2, M3, and M4 and a capacitor C1. In Patent Document 1, in the case where a signal at high level is output as a signal OUT, a gate of the transistor M1 is made into a floating gate, and a bootstrap operation in which the potential of the gate of the transistor M1 is increased to be higher than a potential VDD by using capacitive coupling of the capacitor C1. To make the gate of the transistor M1 into the floating gate, a transistor (e.g., the transistor M4) connected to the gate of the transistor M1 is turned on by making the potential difference between gate and source of the transistor (hereinafter, the difference is referred to as Vgs) 0 V.
Further, in the case where a signal at low level is output as the signal OUT, a signal at high level is input as a signal IN, and thus the transistors M2 and M3 are turned on.